Kth Smallest Element in a BST

该题的思路很简单，就是对BST进行先序遍历，找到第k个数的时候返回。这里借助栈用迭代实现，递归的代码更简单，没有尝试。

class Solution {
public:
    int kthSmallest(TreeNode* root, int k) {
        stack<TreeNode *> cache;
        TreeNode *point = root;
        TreeNode *tmp;
        int i = 0;
//先序遍历
        while(point || !cache.empty()){
            while(point){
                cache.push(point);
                point = point -> left;
            }
            if(!cache.empty()){
                tmp = cache.top();
                i++;
                if(i == k)
                    return tmp -> val;
                cache.pop();
                point = tmp -> right;
            }
        }
    }
};

Kth Smallest Element in a BST

原文：http://blog.csdn.net/ny_mg/article/details/46851163